The patent literature is replete with disclosures for the preparation and use of alkyl succinic anhydrides. There are disclosures with regard to reaction products of succinic anhydrides with various alkyl moieties including wax, paraffins and the like. For example, U.S. Pat. No. 4,041,056 discloses wax anhydride compounds and uses in carbon paper, inks, polishes and the like. U.S. Pat. No. 3,449,236 discloses wax-maleic anhydride reaction products and use as dewaxing aids in separation wax from petroleum oil. U.S. Pat. No. 2,231,498 describes lubricants which contain alkyl substituted succinic acid compounds which are produced as the maleic anhydride adduct of a high molecular weight unsaturated hydrocarbon polymer. U.S. Pat. No. 4,486,324 describes hydraulic fluids which contain a hydrocarbyl substituted succinic acid which is produced by reacting an olefinically unsaturated aliphatic hydrocarbon with maleic anhydride which is then hydrolyzed to form the acid. U.S. Pat. Nos. 4,554,080, 3,923,669, 3,428,561, 4,450,281, and 4,086,251 all disclose alkyl or alkenyl substituted anhydrides which are produced by the reaction of maleic anhydride with a hydrocarbon and their use in hydraulic oils and hydraulic fluids. U.S. Pat. Nos. 3,030,387 and 3,590,076 specifically describe wax-anhydride reaction products. U.S. Pat. No. 4,041,056, mentioned above, also describes reaction products of wax anhydride compounds, together with further reaction with polyamines. Both U.S. Pat. Nos. 4,041,056 and 3,590,076 refer to U.S. Pat. No. 3,030,387 as describing the basic process for preparation of such products. As disclosed in U.S. Pat. No. 3,030,387, these products are produced by reaction of an alkane or cycloalkane with maleic anhydride in the presence of a peroxide free-radical initiator catalyst. Excess alkane or cycloalkane is ordinarily employed in up to a ten fold in molar excess in order to ensure as complete reaction as possible. The working examples support this manner of carrying out the reaction. U.S. Pat. Nos. 4,041,056 and 3,590,076 are directed to coupling of these materials with polyfunctional poly alcohols in U.S. Pat. No. 3,590,076 and with polyamines in U.S. Pat. No. 4,041,056. Both of these patents present general structural formulae in column 1 for products which are said to be representative of the wax-anhydride compounds produced according to this process. However, the present invention differs in several important respects: (A) Both U.S. Pat. Nos. 4,041,056 and 3,590,076 state in column 3 that liquids and soft solids do not yield the products of their respective inventions. Further, both cited patents state in their first claim that the wax reactant has a melting point of at least 150.degree. F. and a penetration of from 0+ to about 50. The present invention pertains only to liquid, soft solid, and waxy hydrocarbons melting below 150.degree. F. While U.S. Pat. No. 3,030,387 teaches liquid and low melting hydrocarbon reactants, it pertains to and claims only monoanhydride products, obtained with excess molar ratios of hydrocarbon. (B), Both U.S. Pat. Nos. 4,041,056 and 3,590,076 teach in their examples, Tables 1 and 2, and first claims, the use of maleic anhydride to wax mole ratios of 1.5 or less. The present invention pertains only to higher maleic anhydride to wax mole ratios. (C), Table 1 of both patents teaches products with acid numbers of less than 50. The present invention pertains generally to products with acid numbers above 400. (D) Both patents teach in column 3 wax-soluble, methanol-insoluble products. The products of the present invention are insoluble in wax and soluble in polar solvents such as methanol, acetone, and aqueous solutions.
The present invention provides polyanhydrides produced by the reaction of maleic anhydride or equivalent anhydrides with long chained hydrocarbons, which polyanhydrides are distinguished from and advantageous over the prior art products discussed above. The terms "polyanhydride" or "polysuccinic anhydrides" as used herein, refer to multiple succinic anhydride groups substituted onto a hydrocarbon and are not to be confused with polymer connotations. By virtue of the excellent characteristics of the products of this invention, the solubility properties and physical form distinguish the products from the prior art and make such products advantageous as emulsifiers, surfactants or dispersants in hydraulic fluid compositions and as epoxy resin curing agents.